This invention relates in general to underground drilling/boring systems and methods, and more particularly to a method and apparatus for automatically controlling the thrust force incident on one or more drill rods forming the drill string of the underground boring system.
Utility lines for water, electricity, gas, telephone, cable television, digital communication and computer connections are among the many types of physical lines or cables often run underground. Generally, it is desirable to bury these lines for reasons of safety and aesthetics. In many situations, the underground utilities can be buried in a trench, which is subsequently back-filled. Although useful in areas of new construction, the burial of utilities in a trench has certain disadvantages. In areas supporting existing construction, a trench can cause serious disturbance to structures or roadways. Further, there is a high probability that digging a trench may damage previously buried utilities, and that structures or roadways disturbed by digging the trench are rarely restored to their original condition. Also, the trench poses a danger of injury to workers and passersby.
The general technique of boring a horizontal underground hole has been developed to overcome the disadvantages described above, as well as others unaddressed when employing conventional trenching techniques. In accordance with such a general horizontal boring technique, also known as microtunnelling or trenchless underground boring, a boring system is positioned on the ground surface. The boring system is arranged to drill a hole into the ground at an oblique angle with respect to the ground surface. Fluid is flowed through the drill string, over the boring tool, and back up the borehole in order to remove cuttings and dirt. After the boring tool reaches the desired depth, the tool is then directed along a substantially horizontal path to create a horizontal borehole. After the desired length of borehole has been obtained, the tool is then directed upwards to break through to the surface. A reamer is then attached to the drill string which is pulled back through the borehole, thus reaming out the borehole to a larger diameter. It is common to attach a utility line or conduit to the reaming tool so that it is dragged through the borehole along with the reamer.
The length of a desired bore may be substantial. In order to create a drill string of sufficient length to create the desired bore, many fixed lengths of drill rods may be attached end-to-end. More particularly, a first drill rod is placed on the machine rack and forced into the ground. A subsequent length of drill rod is placed on the machine and coupled to the first length, generally via threads on each drill rod. The combined length is then further forced into the ground. In order to form a complete bore, numerous drill rods are added in this fashion during the boring operation. As rods are added, the drill string length and the resulting bore length increases.
An operator of a conventional underground boring tool typically modifies the rate of boring tool advancement. The thrusting force can be manually varied by the operator based on many parameters including the desired speed of drill string advancement and soil conditions. However, in an effort to maximize drilling speed, an operator may apply more thrust force than can safely be applied to one or more of the drill rods without its becoming damaged or destroyed. The operator will be unaware of how much thrust force can be applied without causing such damage. Therefore, the operator may apply too little thrust force which results in drilling inefficiencies, or may alternatively apply too much force and damage the drill string.
There is a need in the underground boring industry to minimize such problems and assist drilling operators in carrying out drilling processes. Additionally, there continues to be a need for an improved underground boring machine that provides for high boring efficiency through varying ground conditions, yet minimizing delays and costs associated with drill string damage, without depending on human intervention. The present invention fulfills these and other needs, and provides additional advantages over the prior art.
To overcome limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention generally discloses a system, apparatus and method for automatically limiting the thrust force applied to a drill string during an underground boring process, in order to prevent the deformation or collapse to the drill rods due to reaching the xe2x80x9cyieldxe2x80x9d point of the rods.
In accordance with one embodiment of the invention, a method is provided for controlling the underground transit of a drill string. One or more drill string characteristics that influence the yield point of the drill string, or portions of the drill string, are determined. The yield point of the drill string or portion is computed, where the yield point is computed as a function of the drill string characteristics. The thrust force imparted to the drill string is adjusted in response to the computed yield point.
In accordance with another embodiment of the invention, a method is provided for controlling the subterranean advancement of one or more drill rods forming a drill string. An unsupported (or relatively little-supported) length of the drill string is measured. For example, one or more drill rods forming the drill string that has an unsupported portion may be measured. The yield point of the drill string portion is calculated as a function of the unsupported length of the drill string. The thrust force imparted to the drill string is limited to a maximum allowable thrust force such that the yield point will not be reached.
In accordance with yet another embodiment of the invention, a method is provided for controlling the movement of a drill string, where the drill string is moved along an underground path. A bend radius is determined for at least a portion of the drill string along the underground path. The yield point of the drill string portion is computed as a function of the bend radius. The thrust force imparted to the drill string is adjusted in response to the computed yield point.
In accordance with another embodiment of the invention, a system for controlling the underground transit of a drill string is provided. The system includes a thrust engine to generate a thrust force for advancing the drill string. At least one drill string sensor is provided to sense drill string characteristics impacting a yield point the drill string or drill string portion. A controller is coupled to the drill string sensors and the thrust engine. The controller calculates the yield point of the drill string portion as a function of the drill string characteristics, and generates a thrust force adjustment signal based on the calculated yield point. The magnitude of the thrust force is dependent on the thrust force adjustment signal.
In still another embodiment, a horizontal drilling machine for directionally drilling a drill string into the ground is provided. The drill string includes a plurality of elongated rods threaded together in an end-to-end fashion. The machine includes a track, a rotational driver for rotating the drill string about a longitudinal axis of the drill string, and a thrust mechanism for propelling the rotational driver along the track. Also included is a thrust limiter that prevents the thrust mechanism from applying a thrust load to the drill string that exceeds a thrust load limit established at least in part by a buckle point of a drill string portion. The thrust load limit is less than a maximum thrust load that can otherwise be generated by the thrust mechanism.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.